[TYPO3-english] typoscript about "page.includeLibs.some_random_id_string"

[typo3 study]

Hi,

In template->setup, typoscirpt, I saw below code:
page.includeLibs.some_random_id_string = fileadmin/userfunctions.php

What is the meaning of this code? what is the difference between this one
and page.includeLibs = fileadmin/userfunctions.php ?

Thanks.

Tom